The present invention relates to linear guide devices, for example, for use in linearly moving the table of a machining tool, and more particularly to a linear guide device comprising a straight guide rail and a movable body approximately inverted U-shaped in cross section and movable as fitted over the guide rail.
The terms "front," "rear," "left" and "right" are used herein and in the appended claims with respect to the direction of movement of the movable body.
Linear guide devices of the above-mentioned type heretofore known include one which comprises a straight guide rail, and a movable body having an approximately inverted U-shaped cross section and movable as fitted over the guide rail. Each of opposite side surfaces of the guide rail and the surface of each of opposite legs of the movable body which surface is opposed to the rail side surface are each formed with a ball guide groove having a circular-arc portion. The ball guide grooves are equal in the curvature of the circular-arc portion over the entire length thereof and provide a forward ball passage. Each of opposite legs of the movable body is formed with a return ball passage. Each end of the forward ball passage is in communication with the corresponding end of the return ball passage through a reverse passage formed in each end of the movable body to form a circular ball channel. A plurality of balls are enclosed in the circulation ball channel, rollable between the movable body and the guide rail, and in point contact with the circular-arc portions of the ball guide grooves when in the forward ball passage of the circulation channel. A line through the center of curvature of the movable body ball guide groove is in parallel to a line through the center of curvature of the guide rail ball guide groove.
With the known device described above, the balls are rolalble in point contact with the circular-arc portions of the two grooves, so that the line through the center of curvature of the movable body guide groove is naturally positioned closer to the guide rail than the line through the center of curvature of the guide rail guide groove. Further when in the forward ball passage, the ball is preloaded in a direction through the points of contact of the ball with the ball guide faces.
With the linear guide device described, the forward ball passage is a loading zone, and the return ball passage and the reverse ball passage are nonloading zones. In the loading zone wherein the ball is loaded, the ball is elastically brought close to the circular-arc portions of the grooves and elastically deformed by contact with these portions. In the nonloading zone, there is a clearance inside the groove circular-arc portions around the ball for the ball to freely roll along, and the ball is free of deformation. Accordingly, the ball is abruptly relieved of the load acting thereon when entering the nonloading zone from the loading zone, whereas the ball is abruptly loaded heavily when entering the loading zone from the nonloading zone. In either case, the ball deforms suddenly. Consequently, when the balls travel between the loading zone and the nonloading zone even under a constant load, the movable body will not advance straight properly because the number of loaded balls changes abruptly, entailing the problem of causing vibration to the movable body.
To gradually decrease the load on the ball as the ball rolls along toward the reverse passage, therefore, a load reducing region is conventionally formed at each of longitudinally opposite ends of the ball guide groove of the movable body, for example, by grinding the end portion of the guide groove after the groove has been formed by grinding the movable body. In the load reducing region, the line through the center of the movable body ball guide groove is deviated, when seen in cross section, on a straight line extending from the above line through the points of contact of the ball with the circular-arc portions of the ball guide grooves in a maximum loading region, and is thereby gradually brought closer to the line through the center of the guide rail ball guide groove toward the reverse passage.
When in the forward passage, the balls are then all preloaded only in the direction through the points of contact of the ball with the two ball guide grooves, i.e., in the same direction. This gives rise to problems. If the balls are loaded in a direction other than the preloading direction, especially in a direction orthogonal to the line through the points of contact, a reduced loading capacity or rigidity will result, and the movable body undergoes greater vibration.